The present invention relates to a highly toughened, sintered mass of zirconia containing ZrO.sub.2 as the main component.
The greatest disadvantage of ceramic materials was their poor bending strength. An appreciable number of experts in the art have been involved in this problem, since improvements in bending strength have been considered to make it possible to use, with marked effect, those materials for cutting tools and artificial aggregates as well as parts for internal combustion engines.
For instance, Japanese Patent Kokai-Publication No. 55-140762 entitled A CUTTING TOOL MATERIAL OF THE ZIRCONIA TYPE discloses sintered zirconia partially stabilized with oxides of Y, Ca, Mg, etc., and teaches that it has a crystal phase including 60-95% by weight of the tetragonal and isometric systems in total. An article by J. S. Reed published in "Ceramic Bulletin", Vol. 55, pp. 717 (1976), U.S.A., describes that high-strength ZrO.sub.2 sintered masses are obtained by co-precipitating a mixture of ZrOCl.sub.2 and YCl.sub.3 and calcining the resulting powder, then sintering the fine calcined powder of ZrO.sub.2 stabilized with Y.sub.2 O.sub.3. However, none of these materials are found to be satisfactory in respect of the strength. Thus, there is a strong demand for further increase in the strength, which will enable wider utilization coverage.